Curie point depth from spectral analysis of aeromagnetic data for geothermal reconnaissance in Afghanistan

Abstract

The geologic setting of Afghanistan has the potential to contain significant mineral, petroleum and geothermal resources. However, much of the country's potential remains unknown due to limited exploration surveys. Here, we present countrywide aeromagnetic data to estimate the Curie point depth (CPD) and to evaluate the geothermal exploration potential.CPD is an isothermal surface at which magnetic minerals lose their magnetization and as such outlines an isotherm of about 580 °C. We use spectral analysis on the aeromagnetic data to estimate the CPD spatial distribution and compare our findings with known geothermal fields in the western part of Afghanistan.The results outline four regions with geothermal potential: 1) regions of shallow Curie point depths (∼16–21 km) are located in the Helmand basin. 2) regions of intermediate depths (∼21–27 km) are located in the southern Helmand basin and the Baluchistan area. 3) Regions of great depths (∼25–35 km) are located in the Farad block. 4) Regions of greatest depths (∼35–40 km) are located in the western part of the northern Afghanistan platform. The deduced thermal structure in western Afghanistan relates to the collision of the Eurasian and Indian plates, while the shallow CPDs are related to crustal thinning. This study also shows that the geothermal systems are associated with complex magmatic and tectonic association of major intrusions and fault systems. Our results imply geothermal gradients ranging from 14 °C/km to 36 °C/km and heat-flow values ranging from 36 to 90 mW/m2 for the study area.